There is a paucity of measurement tools that adequately assess the development of language and literacy skills in children from diverse linguistic and cultural backgrounds. Rather, professionals utilize measures that are considered psychometrically sound relative to the normative population but are not sensitive to developmental differences between monolingual and bilingual speakers, nor standardized on bilingual poulations. This is particularly true in the domain of phonology where quantitative measurement of bilingual phonological development is still in its infancy. Consequently, bilinugal children are often identified as having a phonological disorder when their development is following a different, but not disordered pathway. Other times, biingual children with lingustic difficulties are ignored due to fear of over identification of disorders in minority populations. The aims of this project are to draw upon recent advances in phonological theory and bilingual research 1) To develop a valid and reliable measure to identify phonological disorder in bilingual Spanish and English speaking children and to distinguish disorder from phonological variation due to typical bilingual phonological development and change; 2) To assess change in multiple aspects of bilingual children's phonological development in order to identify characteristics of young bilingual children's phonological systems that are indicators of disorder later in development and 3) To develop training materials and field test a phonological screening tool for use by speech language pathologists, that is based the instrument developed under Aim 1. A mixed cross-sectional and longitudinal design will be used to develop a measure of the phonological development of children ages 3 to 6 years, who speak Mexican, Puerto Rican and Cuban dialects of Spanish. Measures that accurately assess the needs of bilingual chidlren are critically important in order to assure accurate diagnosis of disorders in young children.